Mu Chenyan didn't know much about the love life of Xiang Wai and Xiang Weimin. Even if she had been keeping an eye on their situations, it mostly involved things related to their health and their career. She wasn't overbearing enough to try to control everything. Yes, she was overbearing at some level but she wasn't a complete wacko. Not just yet!
And that's why she didn't know that Xiang Wai had been in a relationship with someone for ten years and it seems she hurt herself. As for why she said she hurt herself instead of saying that she got hurt. The answer was obvious. Xiang Wai had the expectations set high from that relationship that didn't even begin from love.
If that wasn't asking for a heartbreak what was?